1. Field of the Invention
The present invention relates to a brush holding device for an electric motor, and more particularly to a brush holding device for a DC electric motor of small size.
2. Description of the Prior Art
An electric motor is generally divided into two types, i.e., one requiring replacement of brushes and the other requiring no replacement thereby to enjoy a relatively long life. In the brush replaceable type, since the brush replacement is not always performed by those having sufficient knowledge of the construction of the electric motor, it is required that the attachment and detachment of a brush cap be made as easily and surely as possible.
Generally speaking, the brush holding device for the electric motor includes a brush holder mounted to an outer frame, a brush fitted into the brush holder, a coil spring fitted in the brush holder for forcing a brush into contact with a commutator segment, and a brush cap mounted to the outer side of the brush holder for bearing the opposite end of the coil spring to the commutator segment. The electric motor of the brush replaceable type is constructed to have its brush cap removably mounted to the brush holder.
The brush-replaceable type brush holding device according to the prior art is disclosed in, for example, Japanese Utility Model Laid-Open Publication No. 53-123405, wherein the brush holder has, at an open end formed on an inner wall an annular land; whereas, the brush cap has, at a center on an upper side thereof a projection and, at a lower end an annular land. Thus, if the projection of the brush cap is forced into the open end of the brush holder, the land of the brush cap rides over the land of the brush holder so that the brush cap is snugly fitted snapped in the brush holder.
The brush holding device of this snap type has an advantage that the brush cap can be mounted on the brush holder by the single action. However, if the brush cap is to be removed from the brush holder, it is necessary to detach the projection of the brush cap from the opening of the brush holder by means of a suitable tool. As a result of this detachment procedure, the brush replacement is troublesome, and the projection of the brush cap may be broken by the tool.